During 3GPP Release 12, the Long Term Evolution (LTE) standard has been extended with support of device to device (D2D) (specified as “sidelink”) features targeting both commercial and Public Safety applications. Some applications enabled by Rel-12 LTE are device discovery, where devices are able to sense the proximity of another device and associated application by broadcasting and detecting discovery messages that carry device and application identities. Another application is direct communication based on physical channels terminated directly between devices. This new direct D2D interface is sometime designated as PC5, also known as sidelink at the physical layer.
One potential extension for the D2D work is support of vehicle-to-x (V2x) communication, which includes any combination of direct communication between vehicles, pedestrians and infrastructure. V2x communication may take advantage of a network (NW) infrastructure, when available, but at least basic V2x connectivity should be possible even in case of lack of coverage. Providing an LTE-based V2x interface may be economically advantageous because of the LTE economies of scale and it may enable tighter integration of communications between vehicles and the NW infrastructure (V2I), communications between vehicles and pedestrians (V2P), and vehicle-to-vehicle (V2V) communications, as compared to using a dedicated V2x technology. FIG. 1 is a schematic diagram illustrating V2x scenarios for an LTE-based Network.V2I may be provided over cellular LTE, providing wide area coverage and allowing for reuse of existing infrastructure. V2I may also be provided through Road Side Units (RSU) that are LTE pico-nodes. This allows for full integration with cellular LTE. V2V and V2P may either be provided over cellular LTE, which thus allows ITS services to be enabled for legacy smartphones, or over LTE-D2D providing radio-aware integration with cellular LTE.
V2x communications may carry both non-safety and safety information, where each of the applications and services may be associated with specific requirements sets, e.g., in terms of latency, reliability, capacity, etc.
DSRC (Dedicated Short Range Communications) is a two-way short- to medium-range wireless communications capability critical in communications-based active safety applications. It comprises wireless communication channels specifically designed for automotive use and a corresponding set of protocols and standards. The United States Federal Communications Commission (FCC) has allocated 75 MHz of spectrum in the 5.9 GHz band to be used by intelligent transportat systems (ITS) vehicle safety and mobility applications. IEEE 802.11p is an approved amendment to the IEEE 802.11 standard to add wireless access in vehicular environments. It defines enhancements to 802.11 (the basis of products marketed as Wi-Fi) required to support ITS applications. 802.11p is considered for DSRC.
European Telecommunications Standards Institute (ETSI) has defined two types of messages for road safety: Co-operative Awareness Message (CAM) and Decentralized Environmental Notification Message (DENM).
The CAM message is intended to enable vehicles, including emergency vehicles, to notify their presence and other relevant parameters in a broadcast fashion. Such messages target other vehicles, pedestrians, and infrastructure, and are handled by their applications. CAM message also serves as active assistance to safety driving for normal traffic. The availability of a CAM message is indicatively checked for every 100 ms, yielding a maximum detection latency requirement of less than or equal to 100 ms for most messages. However, the latency requirement for Pre-crash sensing warning is 50 ms.
The DENM message is event-triggered, such as by braking, and the availability of a DENM message is also checked for every 100 ms, and the requirement of maximum latency is less than or equal to 100 ms.
The package size of CAM and DENM message varies from 100+ to 800+ bytes and the typical size is around 300 bytes. The message is supposed to be detected by all vehicles in proximity.
The Society of the Automotive Engineers (SAE) also defined the Basic Safety Message (BSM) for DSRC with various messages sizes defined.
According to the importance and urgency of the messages, the BSMs are further classified into different priorities.
FIG. 2 is a block diagram illustrating spectrum allocation at 5 GHz. In Europe, 7×10 MHz channels are currently designated for ITS safety-related services in the 5875-5905 MHz band. In addition, 5905-5925 MHz is identified in ECC Decision (08)01 as potential extension band for ITS, and 5855-5875 MHz is recommended to be made available for ITS non-safety related applications through ECC Recommendation (08)01 ITS services are expected to be primary services deployed on such spectrum. Any other system that wishes allocation as secondary service would then need to ensure that it gives priority to such system. On the other hand, non-safety ITS is not of the same priority and it could potentially be co-primary allocated with other services.
Agenda Item 1.16 of the World Radiocommunication Conference 2019 (WRC-19) considers issues related to wireless access systems (WAS), including radio local area networks (RLAN), in the frequency bands between 5 150 MHz and 5 925 MHz, and take appropriate regulatory actions, including additional spectrum allocations to the mobile service, in accordance with Resolution COM6/22 (WRC-15); as a response, ECC has mandated European Conference of Postal and Telecommunications Administrations (CEPT) to do such compatibility studies. These are being included in ETSI TR 103 319.
Currently, the ETSI ITS standards consider DSRC technologies as the baseline for ITS. At the same time, a new Work Item (WI) has been approved in 3GPP to define LTE for ITS (both safety and non-safety), 3GPP RP-152293. Both technologies are then of the same priority and will need to co-exist in the same spectrum. LBT
Listen-Before-Talk (LBT) is defined in ETSI ITS, EN 302 571. Listen-Before-Talk in conjunction with preamble detection requires the device which wishes to transmit to listen to the channel and transmit if the measured level in such channel is below a pre-defined threshold.
In addition, TR 103 319 proposes the use of Preamble detection to allow RLAN devices to detect DSRC.